Off road equipment such as lift trucks, skid steer loaders, compact excavators, and the like, often utilize a spring supported seat to isolate the seat occupant from vibration during vehicle operation. Such cushioning usually utilizes extension or compression springs which support the occupant's weight. However, because the range of the seat occupant's weight is often in excess of 150 pounds and because of the relatively confined space in these types of vehicles available for the seat, it is not only difficult to configure a seat suspension that fits in such a small space but it is also a challenge to “tune” a spring supported seat suspension to provide optimum comfort. Accordingly, it has been known to employ seat suspensions utilizing extension or compression springs wherein the biasing force imposed by the springs on the seat structure is adjustable.
U.S. Pat. No. 5,601,338 discloses a vehicle seat structure that includes a mechanical spring type adjustable vehicle seat suspension. In this patent, the seat is pivoted at its forward edge, and the rear edge is supported by a pair of extension springs. An adjustable slide located upon a lever arm is interposed between the springs and the rear seat portion where the position of the slide is adjusted to vary the extent of spring biasing force by changing the location of the application of the biasing force relative to the lever. While this adjustable seat suspension construction enables adjustment for a wide weight range of vehicle operators, only the forward pivoting seat bottom is suspended, which reduces the effectiveness of the suspension system and results in relative motion between the occupant and seat backrest. This can cause a vehicle operator to experience unwanted discomfort during use and operation.
U.S. Pat. No. 6,186,467 discloses an improved adjustable mechanical spring type seat suspension where the entire seat frame is mounted on a scissors linkage and supported by the suspension. By linking the seat frame to the suspension, both the seat back and seat bottom move in unison during suspension operation, comfort is enhanced because both occupant support and vibration isolation is improved. The vehicle suspension is also adjustable such that it can be adjusted for a limited range of vehicle operator weights.
While these compact mechanical spring type vehicle seat suspensions provide relatively low collapsed height, are compact in size, and are relatively economical in cost and maintenance, improvements nonetheless remain desirable. For example, vehicle operator adjustment of a mechanical spring type seat suspension can be challenging, particularly while the vehicle operator is sitting. In addition, as the vehicle operator weights continue to increase, mechanical spring type seat suspensions are not readily configurable to provide support and enable adjustment over an increasingly wider weight adjustment range.
What is needed is an improved vehicle seat suspension which is well suited for use in vehicle seat suspension application where a low seat index point (SIP) is required or desired, which offers improved ease of adjustment along with a greater adjustment range, and which is adaptable for use in a wide variety of seating applications.